The use of polyurethane elastomer formulations in the manufacture of molded products by a variety of techniques which include injection molding, rotational molding or casting and reaction injection molding (RIM) is widely known. These formulations for use in various applications are formed by reacting a polyisocyanate with a polyol and, in some cases, then chain extending with a diamine or polyol chain extender to provide rigidity. Typically, such formulations will utilize an aromatic diisocyanate, a polyol, and a diamine chain extender.
In the processing of urethane formulations to form molded products substantial attention to the selection of the isocyanates and chain extenders is necessary to achieve the desired end properties. In the manufacture of large units, particular attention has to be given to the chain extender, not only in terms of its contribution to the end properties of the product, but also its contribution in terms of the processing characteristics. Aliphatic and many aromatic amine chain extenders are highly reactive and gelation of the urethane formulation occurs prior to completion of the molding operation. In their active state they are unsuited for those applications. With aromatic amines, it is possible to incorporate groups which sterically hinder the amine molecule or to incorporate electronegative groups which make the molecule less reactive. These less reactive amines then may be used in the particular molding applications.
Molded products for use in applications such as motor mounts, shock absorber, and vibration dampeners must have an ability to resist heat build up due to internal frictional causes and they must be impact resistant. Tires either for passenger car service or larger tires as, for example, trucks and farm tractors, have to meet rigid requirements in terms of impact resistance, abrasion resistance and thermal resistance, etc. Tires are also exposed to heavy flexing and internal heat is generated which can cause thermal degradation of the polymer. To withstand this flexing the polymers must have a low hysteresis in order to avoid excessive heat generation. Further because tires are of significant size, they present an additional problem with respect to their manufacture. The processing techniques have to be closely mentioned so that gelation does not occur prior to filling the mold.
Representative patents showing some urethane formulations, and particularly diamine chain extenders as well as applications and molding techniques for tire formulations, are as follows:
U.S. Pat. No. 2,173,884 shows the manufacture of a tire composition having a tread section of polyester-diisocyanate elastomer bonded with an adhesive formulation of polyalkylene ether glycol diisocyanate elastomer to a rubber tire stock. The polyester diisocyanate elastomer was formed by reacting adipic acid with ethylene and propylene glycol with 4,4'-methylene diphenyl diisocyanate.
U.S. Pat. No. 4,044,811 shows the manufacture of a laminated tire which utilizes a polyurethane formed from a prepolymer of toluene diisocyanate and a polyalkylene glycol such as poly(tetramethylene ether glycol) and a diamine chain extender such as ethylene diamine, methylene-bis-(2-chloroaniline) (MOCA) and the like.
U.S. Pat. No. 4,090,547 shows the manufacture of a urethane tire wherein the urethane is formed by reacting a prepolymer of poly(tetramethylene ether glycol) and toluene diisocyanate having an isocyanate content of about 4% with metaphenylene diamine as a chain extender. Similar formulations utilize MOCA as the chain extender.
There are numerous references showing the manufacture of polyurethane resins for various applications using a variety of diamine chain extenders. Such references include:
U.S. Pat. No. 3,563,906 discloses formaldehyde condensed amine curing agents for liquid isocyanato-terminated polyurethanes. Representative amine curing agents include hindered or negatively substituted aromatic diamines such as methylene bis-chloroaniline, and dichlorobenzidine. The formaldehyde condensed amines have moderate reactivity and a limited tendency to crystallize under operating conditions.
U.S. Pat. No. 3,194,793 discloses polyurethane mixtures cured with aromatic primary and secondary amines. Representative amines include 4,4'-methylene-bis(2-chloroaniline) (MOCA), diphenyl propylenediamine, diamino diphenyl ether, naphthalene diamine, toluene diamine, various halogenated and alkoxylated benzidines, e.g. dimethoxy benzidine and dichlorodimethyl benzidene.
U.S. Pat. No. 4,017,464 discloses polyurethane compositions formed by reacting toluene diisocyanate with polytetramethylene ether diol and then cross-linking with a diamino diphenyl disulfide curing agent. Such compositions are alleged to be well suited for tire manufacture.
U.S. Pat. No. 4,002,584 discloses urethane elastomers formed by reacting a long chain polyol with an organic diisocyanate and a halogenated aromatic diamine such as methylene-bis-dichloroaniline, dichlorodibromodiaminodiphenyl methane, tetrabromobenzidine and other halogenated aromatic diamines.
U.S. Pat. No. 3,846,351 discloses a method for preparing flexible polyurethane foams by reacting a polyether polyol with an organic diisocyanate and cross-linking with a dialkyl paraphenylene diamine. Examples of chain extenders include diisopropylphenylenediamine, di-sec butyl-paraphenylene diamine.
U.S. Pat. No. 4,254,272 discloses polyurethanes formed by reacting an organic diisocyanate with a polyol and then curing with a substituted aromatic diamine consisting of diamino-tert-alkyl benzoates and diamino-tert-alkyl benzonitriles. Specific examples of the diamines include methyl diamino-tert-butyl benzoate; octadecyl diamino-tert-butyl benzoate and comparable alkyl benzonitriles.
U.S. Pat. No. 3,736,295 discloses the preparation of polyurethane elastomers by reacting an organic diisocyanate with an organic polyol utilizing an aromatic diamine containing ether groups and chlorine atoms in the ortho position as a chain extender.
U.S. Pat. No. 3,752,790 discloses various amine curing agents for liquid polyurethanes having free isocyanate groups. Examples include dichlorotoluene diamine and chlorotoluene diamine as the amine curing agents. The chlorinated toluene diamines are alleged to improve hardness and modulus of the urethane composition.
U.S. Pat. Nos. 4,048,105; 4,218,543 disclose molding urethane formulations by the technique of reaction injection molding (RIM). The systems utilize a formulation consisting of a quasi-prepolymer consisting of the reaction product of a low molecular weight diol or triol and an organic isocyanate e.g. methylene bis(4-phenyl isocyanate) with a polyol blend consisting of polyol, amine chain extender and catalyst. Examples of the amine chain extenders include the unhindered aromatic polyamine, such as methylene dianiline (MDA). The '543 patent uses an alkylated diamine, such as diethyltoluene diamine as a chain extender in a RIM process. These alkylated aromatic diamines result in extending gelation time as compared to the unhindered aromatic diamines. In practice the isocyanates and amine chain extenders were selected on the basis of reactivity and performance. Reactivity was altered by using an inactive isocyanate with an active diamine or vice versa. Performance was generally good because of the inherent abrasion resistance and toughness of the urethane polymer. However, even though urethane polymers have good physical properties and are suited for application in tires, they have enjoyed little commercial success. They simply have not competed with rubber for tires in terms of high speed performance and cost.